14-1
14 Acoustic Power Principle
14.1 Concerns with Bioeffects
Diagnostic ultrasound is recognized as being safe. In fact, there have been no reports of
injuries to patients caused by diagnostic ultrasound.
It cannot be stated categorically that ultrasound is 100% safe. Studies have revealed that
ultrasound with extremely high intensity is harmful to body tissues.
Diagnostic ultrasound technology has made a great leap forward during the last several years.
This rapid advance has generated concerns about the potential risk of bioeffects when new
applications or diagnostic technologies become available.
14.2 Prudent Use Statement
Although there are no confirmed biological effects on patients caused by exposures from
present diagnostic ultrasound instruments, the possibility exists that such biological effects
may be identified in the future. Thus ultrasound should be used in a prudent manner to
provide medical benefit to the patient. High exposure levels and long exposure times should
be avoided while acquiring necessary clinical information.
14.3 ALARA
It is required to practice ALARA (As Low As Reasonably Achievable) when using ultrasound
energy. Practicing ALARA ensures that the total energy level is controlled below a low enough
level at which bioeffects are not generated while diagnostic information is being accumulated.
The total energy is controlled by output intensity and total radiation time. The output intensity
necessary for examinations differs depending on the patient and the clinical case.
Not all examinations can be performed with an extremely low level of acoustic energy.
Controlling the acoustic level at an extremely low level leads to low-quality images or
insufficient Doppler signals, adversely affecting the reliability of the diagnosis. However,
increasing the acoustic power more than necessary does not always contribute to an increase
in quality of information required for diagnosis, rather increasing the risk of generating
bioeffects.
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